1. Field of the Invention
The present invention generally relates to a data sending/receiving system and method, and more particularly to a data sending/receiving system and method, capable of downloading and streaming data in an environment in which no positive data transmission can be assured. Also, the present invention is directed to an information providing apparatus and method, and a data receiving apparatus and method suitable for use in the data sending/receiving system.
This application claims the priority of the Japanese Patent Application No. 2002-195017 filed on Jul. 3, 2002, the entirety of which is incorporated by reference herein.
2. Description of the Related Art
Recently, the distribution of AV (audio and visual) contents such as image data, music data, etc. over the Internet has become popular. The modes of data distribution typically includes so-called “downloading” by which the user acquires an AV content as a file and “streaming” by which the user can view and listen to AV content data stored in a server and reproduce the data while the data is being received.
In case content data is sent and received via the Internet, especially, in case the data is downloaded (especially, for buying or selling), the data has to be free from missing (defect). On this account, a protocol which assures a positive data transmission, such as TCP (transmission control protocol), is used as far as possible for positive data sending and reception over a low-reliability transmission channel such as the Internet. TCP includes a protocol for recovering the initial sent sequence of the packets having arrived in a different sequence due to a condition of the network, and requesting for resending of packets not sent due to occurrence of any error, thereby implementing a positive data transmission.
On the other hand, the content data distribution via a network, such as audio on demand (AOD), video on demand (VOD) or the like, uses the “streaming” technique for the purpose of natural sound or image reproduction since the streaming assures a real-time data transmission.
TCP, if applied in a data transfer which has to be done on the real-time basis, will cause the data transfer to be less real-time because of a resending procedure etc. So, UDP (user datagram protocol) is used in the data transfer to assure that the data can be transferred on the real-time basis although it will sacrifice the positiveness of the data transfer to some extent.
However, the UDP-based data transmission enables a real-time data transfer for streaming but will not actually make it possible to receive all packets. Often in distribution of an AV content such as a music software over the Internet, the user once confirms the AV content concerning its contents by streaming and then downloads the full AV content if he or she wants to buy.
In the above case, the user acquires almost all data, that are not full, by streaming in the confirmation of the contents of the AV content, but he has to download all the data for buying them. Also, in almost all case, the user wants to reproduce (stream) the contents of the acquired AV content immediately.
Downloading the content of which the majority has been acquired by such streaming is not only a large burden to the transmission channel and server but obliges the user to make a vain payment of connection fees.